Pros
Constant Contact uses many interesting computing technologies to deliver their services. It's a business that really cares about improving the business of its customer base of small businesses and non-profit organizations. There's a tremendous focus on making the customer experience "great!". The software engineering and operations teams deliver value to the organization by applying many of the latest Open Source Software. The CTO is progressive in his approvals of new technology for solving problems - no "tech-religion" constraints here. Mostly a Java/JEE/relational database shop, but you'll also find Ruby-on-RAILS, NoSQL persistence, and mobile web apps here, too. The culture is fun. Beer carts on Friday afternoon and tension relieving nerf battles throughout the day. Everyone pulls the rope in the same direction. A good place to grow professionally.
Cons
Lots of process and too many meetings, however everyone tries to make them lightweight. As with any growing business in a market it helped to make, trying to find the right mix of products and services can be difficult. Software Engineering in this environment comes with its frustrations. At times it seems engineering isn't allowed to take development to it's logical conclusion, but that could be an engineering group issue. A stronger engineering voice could better influence priorities.